J3/15-134r1
To: J3
From: Malcolm Cohen
Subject: Submodules and recursive USE
Date: 2015 February 24

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NUMBER: F08/0128
TITLE: Is recursive USE within a submodule permitted?
KEYWORDS: SUBMODULE, USE
DEFECT TYPE: Clarification
STATUS: J3 consideration in progress

QUESTION:

Consider
  Module m1
    Real x
  End Module
  Submodule(m1) subm1
    Use m1
  End Submodule

Q1. The module m1 is referenced from within one of its own
    submodules.  Is this standard-conforming?

Note that the "submodule TR", Technical Report 19767 contains, an edit
with the normative requirement:
  "A submodule shall not reference its ancestor module by use
   association, either directly or indirectly."
along with a note which says
  "It is possible for submodules with different ancestor modules to
   access each others' ancestor modules by use association."
It also contains an edit to insert the direct reference prohibition
as a constraint.

However, none of this text appears in ISO/IEC 1539-1:2010.

The Introduction simply comments that submodules are available, but
not that they have been extended beyond the Technical Report that
created them.

Also, consider

  Module m2
    Real,Private :: a
    Real,Protected :: b
    ...
  End Module
  Submodule(m2) subm2
  Contains
    Subroutine s
      Use m2
      Implicit None
      a = 3
      b = 4
    End Subroutine
  End Submodule

In submodule SUBM2, procedure S references M2 by use association.
Use association does not make "A" accessible.

Q2. Is "A" still accessible by host association?

Also, procedure S attempts to assign a value to B, which is accessed
by use association, but has the PROTECTED attribute.  Normally, this
attribute prevents assignment to variables accessed by use
association.

Q3. Is the assignment to "B" standard-conforming?

DISCUSSION:

The requirement appears in the early drafts of Fortran 2008, up to
08-007r1, then it was modified by paper 08-154r1 creating a UTI
(because the modification was broken), and finally the requirement was
completely removed by paper 09-141.

ANSWER:

A1. Yes, the example is conforming.  An edit is supplied to add this
    extension to the Introduction, and to add normative text to clause
    11 to make this completely unambiguous.

A2. Yes, A is still accessible by host association.
    Subclause 16.5.1.4 paragraph 2 states
      "If an entity that is accessed by use association has the same
       nongeneric name as a host entity, the host entity is
       inaccessible by that name."
    This does not apply since A is not being accessed by use
    association (because it is PRIVATE), therefore A can still be
    accessed by host association.
{J3 note: no edit necessary here.}

A3. No, the assignment to B is not conforming as it violates
    constraint C551 which states
      "A nonpointer object that has the PROTECTED attribute and is
       accessed by use association shall not appear in a variable
       definition context..."
    An edit is provided to add an explanation of this.

EDITS:

[xv] Introduction, p2, first bullet,
  After "Submodules provide ... for modules."
  Insert new sentence
    "A submodule can reference its ancestor module by use
     association."

[100:12] 5.3.15 PROTECTED attribute,
         "where it is accessed by host association".

[272:23] 11.2.2 The USE statement and use association, p1,
  After
    "A module shall not reference itself, either directly or
     indirectly."
  Append to paragraph
    "A submodule is permitted to reference its ancestor module by
     use association.  "

[273:2+4] Same subclause, NOTE 11.7, append
  "If a submodule accesses a PROTECTED entity from its ancestor
   module by use association, use of that entity is constrained by
   the PROTECTED attribute, e.g. if it is not a pointer it cannot
   appear in a variable definition context.".

SUBMITTED BY: Malcolm Cohen

HISTORY: 15-134   m206 F08/0128  Submitted
         15-134r1 m206 Revised edits.

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